I can't remember what turning channels On and Off in WMC actually does. Just prevents it being played?
In MC, channels can be hidden, or not. If they are hidden they don't appear in any Views, including the guide. (Although even that can be changed, if you want to create a view that shows all channels.) So basically, if a channel has been hidden, it must be unhidden using the Manage Channels function, (or a custom view, or by tagging channels).
There are a couple of ways to view what is scheduled on a channel, and hide the channel if required; one in Standard View, and one in Theatre View.
In Standard View, just go to the Television item in the left navigator, select "All Programs" in the small filter box, and one of the channels in the Channel box. You will be shown what is going to be on that channel for the next 24 hours. You can use the Date drop down list to jump forward to the next 24 hours, then the next, etc., so you can see the whole EPG data set for a channel. It would be nice if it would show everything in the EPG when just one channel is selected, so you could see more programs, but that view is limited to 24 hours (except when using the search box in the upper right corner) so that MC displays the data fast, and a user isn't presented with a huge list. Also showing just 24 hours and jumping forward to future dates means that you just about get one page of data for each day, which is easy to view without getting lost in a big list.
If you see a channel you want to hide, it takes five clicks to do so. Click the "TV Options" button down the bottom, click "Manage Channels", click the "Hidden" checkbox for the channel you want to hide, click "Close" then "OK". Not ideal, but not so bad. Of course you could just write down the channels that you want to hide as you go through the list, and hide them all at once. Not really onerous, for something that you will probably only be doing once.
In Theatre View, display the Guide, review the channel EPG. Yes, you need to scroll left and right to see it all. Once you have found a channel that you want to hide, press enter or click on it with your remote or mouse. You will see the menu at the top with "Watch" highlighted. Move right in the menu to "Tag Channel" and select that. Select "Hide", you will get a warning about unhiding. Select "Hide" again. The channel will stay visible in the Guide until you refresh it. If you hide a channel by mistake, and it is still visible, the above process allows you to unhide the channel. Otherwise the channel can only be unhidden using the "Manage Channels" function.
There is probably a third way that would allow you to select a channel, view all of the EPG for it, and hide or unhide the channel on the one page. It would involve setting up a custom view of the EPG data in MC, which is a recent addition to MC capabilities. If you create a view of the EPG, and Group it by channel, you might be able to get a view that works like TV Series and Episodes, showing the channel in the top frame, and EPG details in the bottom frame. You would then Hide and Unhide the channels by adding or removing the keywords.
I haven't tried that third option. There may be some roadblocks, but maybe those could be removed to give you what you want. However, as I mentioned above, hiding and unhiding channels is probably a once off process, or at least rare, so it isn't going to get the attention that a regularly used function does.
Does this help?